The bandwidth shortage increasingly experienced by mobile carriers has motivated the exploration of the underutilized Millimeter Wave (mmWave) frequency spectrum between 3G and 300G Hz for the next generation broadband cellular communication networks. The available spectrum of mmWave band is two hundred times greater than the conventional cellular system. The mmWave wireless network uses directional communications with narrow beams and can support multi-gigabit data rate. The underutilized bandwidth of the mmWave spectrum has wavelengths ranging from 1 mm to 100 mm. The very small wavelengths of the mmWave spectrum enable large number of miniaturized antennas to be placed in a small area. Such miniaturized antenna system can produce high beamforming gains through electrically steerable arrays generating directional transmissions.
With recent advances in mmW semiconductor circuitry, mmWave wireless system has become a promising solution for real implementation. However, the heavy reliance on directional transmissions and the vulnerability of the propagation environment present particular challenges for the mmWave network. In general, a cellular network system is designed to achieve the following goals: 1) Serve many users with widely dynamical operation conditions simultaneously; 2) Robust to the dynamics in channel variation, traffic loading and different QoS requirement; and 3) Efficient utilization of resources such as bandwidth and power. Beamforming adds to the difficulty in achieving these goals.
Traditional multiple point-to-point protocols used in IEEE 802.11ad beamforming systems are no longer suitable for cellular network in which the relationship between the base station and mobile devices is point to multi-point. In cellular networks, the UL control signaling transmission needs to be organized and be protected at certain level. The base station should help to maintain the quality of UL control signaling transmission. More specifically, IEEE 802.11ad is more suitable for isolated hot spot development but not designed for mobility scenario in cellular network. Non-harmonized beacon transmission interval among access points (APs) introduces higher network discovery latency, which resulting in long network reselection time and thus harmful for service continuity.
A robust control-signaling scheme is thus required to facilitate the beamforming operation in a challenging mmWave environment.